This will be short and sweet. My Smithy lathe/mill has had a flaky speed control potentiometer (pot) for the five years I've owned the machine. Problem is, it's been getting worse. The problem was that when I'd turn the speed control pot to zero, the motor would keep turning slightly, and it would be jerky. I went so far as to contact the company, and they said that I should just use the Stop button every time I want to stop the motor. They did also say a new pot might solve the problem but to still always use the Stop button.
I decided today to see what I could see inside the pot, so I removed it from the machine to take a good look at the innards.
The knob was removed, then the nut was removed, then the pot came out the back side of the panel. The pot wiring had slip connectors that unclipped so I could take the pot to the work bench for further inspection.
After carefully bending the retaining tabs on the backside of the pot (see below photo, red circles), it came apart. Aha! I found corrosion on the ends of the resistance material (although I failed miserably in not getting a photo of the offending gook). After scraping the crud off, I reassembled the pot and clipped the connectors back together for a test run. The motor now stops when the pot is turned down to to zero. Yippy skippy.
The two red circles highlight two of the four tabs holding the pot together (disregard the two tabs poking out, they don't do anything). Once the tabs are carefully bent out of the way (as little as possible), the phenolic resistance wafer can be pried off. Once things are back together, the tabs are carefully bent back into place. If everything goes well, the tabs don't get weak and break off in the process.
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